Ketamine has turned out to be a pretty effective treatment for episodes of severe depression, particularly when there is a risk of suicide; one reason is that it starts having an effect in hours instead of days or weeks like SSRIs do. See Jessica Gilbert's work over at NIH [1]. One of the big focuses of clinical neuroscience is to find features in the brain that will predict treatment responses (to cognitive behavioral therapy, anti-depressants, and so on).

The amygdala is, as is generally known, strongly associated with fear responses, or other negative emotional responses. The subgenual cingulate cortex has been associated with emotion regulation (e.g. down-regulating responses to negative stimuli). I believe that other treatment-prediction studies have found that connectivity between the subgenual cingulate and other brain regions like the amygdala predict treatment responses, so, their result is pretty consistent with the literature as far as I understand.

1. https://scholar.google.com/citations?user=bSXKfxkAAAAJ&hl=en...